In general, photosensitive resin printing plates are divided into those developed with alcohols (alcohol-developing type plates), those developed with alkalis (alkali-developing type plates) and those developed with water (water-developing type plates). At present, water-developing type plates are predominantly used from the viewpoints of easy handling and less problems of waste liquor. As the base polymers of water-developing type photosensitive resin plates, there have been known water-soluble polyvinyl acetate polymers, N-polyvinyl pyrrolidone polymers, polyvinyl alcohol polymers and the like. Most of them have thermosetting properties or less thermoplastic properties. Then, when a resin printing plate is produced by using the base polymer, a solution of the polymer is cast. However, casting is inefficient in comparison with melt molding. On the other hand, when polyamide polymers are used as the base polymers, thermoplasticity can be provided. Therefore, melt molding can be employed and the production can be carried out efficiently. However, the polymers are not suitable for use at a high temperature under a high pressure, for example, as a printing material to produce a matrix which is used for the production of a rubber plate.
That is, in the case of the production of a rubber plate (printing plate, stamp and the like), it is necessary to make a mold for rubber, i.e., a matrix. For this purpose, there has been used phenol resin powder or a matrix board obtained by coating phenol resin on a board. The matrix is produced by using an etched metal plate or a relief made of a photosensltive resin plate as a patrix(original) and pressing the above phenol resin powder or a matrix board with the patrix at a high temperature under a high pressure, for example, at 130.degree. to 150.degree. C. under 20 to 50 kg/cm.sup.2 to cure the phenol resin.
As the patrix, an etched zinc plate of 0.5 to 4 mm in thickness was often used. However, there were problems of handling and treatment of waste liquor. Therefore, recently, a relief made of a photosensitive resin plate of 0.5 to 4 mm in thickness has been often used rather than the etched metal plate. And, as described above, a water-developing type photosensitive resin plate is predominantly used. Particularly, in the photosensitive resin of such a water-developing type plate, there is predominantly used a combination of heat-resistant PVA (polyvinyl alcohol) as a binder and a crosslinking agent. However, PVA contained in this combination is not thermoplastic and, therefore, casting should be employed for producing a thick resin plate and, in the case of the production of a resin plate having such a thickness as thick as 1.5 to 4 mm, there is employed an inefficient process such as repetition of casting several times to pile up layers. Thus, it has been desired to use a thermoplastic polymer having resistance to a high temperature under a high pressure which can be subjected to continuous molding.
In order to provide a thermoplastic polymer with both heat resistance and pressure resistance, several methods can be considered. For example, there is a method wherein a photosensitizing group is introduced into a polymer itself to form a crosslinked polymer. However, there is a problem of insufficient stability during the production of the polymer and a photosensitive resin plate. Further, selection of a crosslinking agent which can provide a high crosslinking density is also considered. However, mere increase in the crosslinking density does not provide sufficient properties. Although Japanese Patent Kokoku No. 47-45584 discloses that the combination of a polyamide and a metal salt of an organic acid having an unsaturated bond as a crosslinking agent provides a composition having improved compatibility, the composition is impractical because storage stability is extremely inferior due to the metal salt and, therefore, heat polymerization is readily caused by a dark reaction. Japanese Patent Kokoku No. 46-9284 discloses a composition composed of a polyamide and a nitroso compound. However, there is no disclosure about a water-developing type plate.